1 / 26

Chlorination Chemistry; Considering Chloramines and Free Chlorine

Chlorination Chemistry; Considering Chloramines and Free Chlorine. Harris County Wastewater Symposium Wastewater Treatment Plants & Bacteria: Strategies for Compliance David Munn, PE April 26, 2011. Chlorination Chemistry; Considering Chloramines and Free Chlorine. Purpose of this Section:

seda
Download Presentation

Chlorination Chemistry; Considering Chloramines and Free Chlorine

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chlorination Chemistry;Considering Chloramines and Free Chlorine • Harris County Wastewater Symposium • Wastewater Treatment Plants & Bacteria: Strategies for Compliance • David Munn, PE • April 26, 2011

  2. Chlorination Chemistry; Considering Chloramines and Free Chlorine • Purpose of this Section: • Explain how ammonia affects your wastewater disinfection capabilities • Provide another tool for reducing bacteria levels in wastewater effluent

  3. Chlorination Chemistry; Considering Chloramines and Free Chlorine • Goals of this Section: • Introduction of Basic Concepts & Chemical Compounds • Discuss the Formation of Chloramines • Disinfection Strength Comparison: Chloramines vs. Free Chlorine • How to Achieve a Free Chlorine Residual?

  4. Introduction of the Cast • Chlorine Compounds: • Chlorine = Cl2 • Through Hydrolysis: Cl2 + H2O ↔ HOCl + H+ + Cl- HOCl ↔ H+ + OCl- • Hyprochlorous acid = HOCl • Hypochlorite ion = OCl-

  5. Introduction of the Cast • Ammonia Compounds: • Ammonia = NH3 • Often referenced as ammonia-nitrogen = NH3-N • Typical wastewater concentration: 25-45 mg/l NH3-N • Chloramine Compounds: • Monochloramine = NH2Cl • Dichloramine = NHCl2 • Tri-chloramine = NCl3 (aka nitrogen tri-chloride)

  6. Is My WWTP Forming Chloramines? • Typical Influent Ammonia Concentration = 30 mg/l NH3-N • Simultaneous Nitrification / Denitrification > 90% removal • 3.0 mg NH3-N requires 27 mg/l Cl2 to achieve breakpoint • Lower NH3-N concentrations at WWTP outfall is a result of NH3-N oxidation by Cl2

  7. Disinfection Performance Comparison: Free Chlorine vs. Chloramines

  8. Disinfection Performance Comparison: Free Chlorine vs. Chloramines

  9. How to Achieve Free Chlorine

  10. Steps to Free Chlorine • Step 1 – Competing Reactions • Organics, Fe2+, Mn2+, and H2S • Result = No Chlorine Residual, No Disinfection Capability

  11. Steps to Free Chlorine • Step 2 – Formation of Mono-chloramine • NH3 + HOCl → NH2Cl (monochloramine) + H2 • Result = Increasing Chlorine Residual, Weak Disinfection Capability

  12. Steps to Free Chlorine • Step 2 – Formation of Mono-chloramine • Theoretical Weight Ratio: 71 mg Cl2 to 14 mg N = 5.1:1 • “Realworld” Weight Ratio: ≈ 6.5:1

  13. Steps to Free Chlorine • Step 3 – Formation of Di- and Tri-chloramines • NH2Cl + HOCl → NHCl2 (dichloramine) + H2O • NHCl2 + HOCl → NCl3 (nitrogen tri-chloride ) + H2O • Result = Lower Chlorine Residual, Lower Disinfection Capability

  14. Steps to Free Chlorine • Step 4 – Breakpoint • Result= Oxidation of all ammonia and competing substances

  15. Steps to Free Chlorine • Step 5 – Formation of Free Chlorine • Result = Begin to Form Free Chlorine; Much Stronger Disinfection Capability

  16. How Much Chlorine is Required? • Reaction Review: • NH4+ + HOCl → NH2Cl + H2O + H+ • NH2Cl + HOCl → NHCl2 + H2O • 0.5NHCl2 + 0.5 H2O → NOH + H+ + Cl- • 0.5NHCl2 + 0.5 NOH → 0.5 N2 + 0.5 HOCl + 0.5H+ + 0.5Cl- Summary of Reactions: NH4+ + 1.5 HOCL → 0.5 N2 1.5 H2O + 2.5 H+ + 1.5 Cl-

  17. How Much Chlorine is Required? NH4+ + 1.5 HOCL → 0.5 N2 + 1.5H2O + 2.5 H+ + 1.5 Cl- Express ammonia as N; Express Chlorine as CL2 Theoretical Weight Ratio = 7.6 mg Cl2 to 1 mg N “Real World” Weight Ratio = 8:1 to 10:1

  18. City of Munnsville Example • Munnsville WWTP • Flow = 1.0 MGD • Influent Ammonia = 30 mg/l NH3-N • Biological Nitrification/Denitrification Capability= 95% NH3-N removal • Chlorination injection rate = 8 mg/l • What is primary chlorine compound?

  19. City of Munnsville Example • Munnsville WWTP • Clarifier Effluent NH3-N Concentration = 30 mg/l * (1 – 95%) = 1.5 mg/l • Chlorine Injection Rate = 8 mg/l • Chlorine : Nitrogen Ratio = 8 mg Cl2 / 1.5 mg N = 5.3 • 5.3:1 < 6.5:1 < 9:1

  20. City of Munnsville Example 6.5:1 5.3:1 9:1

  21. City of Munnsville Example • Munnsville WWTP • Break-point Chlorination Strategy: • Flow = 1.0 MGD • Influent Ammonia = 30 mg/l • Biological Nitrification/Denitrification Capability= 97% NH3 removal • Chlorination injection rate = 9.5 mg/l

  22. City of Munnsville Example • Munnsville WWTP • Clarifier Effluent NH3 Concentration = 30 mg/l * (1 – 97%) = 0.9 mg/l N • Chlorine Injection Rate = 9.5 mg/l Cl2 • Chlorine : Ammonia Ratio = 9.5 mg Cl2 / 0.9 mg N = 10.6 • 6.5:1 < 9:1 < 10.6:1

  23. City of Munnsville Example 6.5:1 10.6 9:1

  24. City of Munnsville Example • Munnsville WWTP • What is Free Chlorine Residual: • Free Chlorine = 1.4 mg/l Cl2

  25. Disinfection Performance Comparison: Free Chlorine vs. Chloramines

  26. Disadvantages to Breakpoint Chlorination • Higher chlorine usage and chemical costs • Possibly higher chlorine residual in effluent • Greater potential for creating disinfectant by-products

More Related